As someone who has recently gained some, though not much, proficiency in this area, I think part of the problem lies with the question itself. We have been convinced by the media to believe that 'flirting' is a clearly definable mode of interaction that socially competent people have no trouble distinguishing from normal interactions. This is false. In my experience people talk about flirting a lot, but are very seldom able to point to instances of it except when there are very obvious body language cues. Almost all men and most women I know have trouble with this. We nerds I think differ more in how uncomfortable we are with the ambiguity, than in our ability to read the situation. You are not alone.

Having a rough road map in your mind does help. Gradual escalation with careful attentiveness to catch signs of discomfort. Just don't take it as an automatic rejection if you see such a sign, it could just mean, 'slow down'.

That said, as a hetero guy I might be operating under a different ruleset. You could probably be quite a lot more forward as a woman, due to not sharing a karyotype with 95% of the world's violent criminals.